1. Field of the Invention
The present invention relates to novel alpha-olefin copolymers and methods of making the same, as well as to methods of nodularizing and cross-linking the copolymer chains to form cross-linked copolymers having particular utilities.
More specifically, the invention relates to novel copolymers of ethylene, another alpha-olefin, at least one halogen-containing monomer, selected from olefinic chlorosilanes and olefinic hydrocarbon halides, and, optionally, one or more non-conjugated dienes.
These copolymers may be in the form of statistical (random) polymers, or they may be segmented in the form of a continuous or discontinuous first segment comprising ethylene and alpha-olefin, and a continuous or discontinuous segment comprising ethylene, alpha-olefin, and the at least one halogen-containing monomer.
In particular, the present invention relates to a process for making these copolymers and, optionally, for coupling them with the use of a cross-linking agent.
Where the copolymer is segmented, the cross-linked copolymers may be in nodular form. In this nodular form, the cross-linking agents may themselves contain functional groups with dispersant character.
The invention further relates to graft and block polymers formed from the copolymer chains, where the at least one halogen-containing monomer is an olefinic chlorosilane or olefinic hydrocarbon halide, and to a process for making such graft polymers.
The copolymers of the present invention are preferably of narrow molecular weight distribution. The composition of the copolymer chains can be "tailored". Among the compositional factors which can be controlled are the sequencing of the monomers and their relative proportions in the chains, portion and frequency of cross-linking, and the composition and positioning of additional substituents within as well as branching from the chain, according to the process of the invention. For example, the olefinic chlorosilanes and olefinic hydrocarbon halides can be confined to specific segments of the chains.
Where a tubular reactor is utilized in the process of the invention, a significant means for accomplishing such tailoring is by varying the locations along the reactor for introducing reactants, as well as the composition, proportions, and flow rates of the reactants.
The noncross-linked statistical and segmented copolymers of the present invention are useful for coating inorganic substrates; they have utility in applications with fiberglass and filled rubber compositions. The noncross-linked statistical and segmented olefinic chlorosilane or olefinic halide copolymers can be coupled to form unusual branched structures; they have utility as intermediates in forming graft and block polymers to prepare such compositions as thermoplastic elastomers and compatibilizers.
Cross-linked statistical copolymers of the present invention are useful in numerous elastomeric applications, such as the preparation of sheeting caulks, sealants, gaskets, etc. The nodular copolymers have utility in lube oil compositions as oil additives.
2. Background Description of Relevant Materials
For convenience, certain terms that are repeated throughout the present specification are defined below:
(a) Inter-CD defines the compositional variation, in terms of ethylene content, among polymer chains. It is expressed as the minimum deviation (analogous to a standard deviation) in terms of weight percent ethylene from the average ethylene composition for a given copolymer sample needed to include a given weight percent of the total copolymer sample which is obtained by excluding equal weight fractions from both ends of the distribution. The deviation need not be symmetrical. When expressed as a single number, for example 15% Inter-CD, it shall mean the larger of the positive or negative deviations. For example, for a Gaussian compositional distribution, 95.5% of the polymer is within 20 wt. % ethylene of the mean if the standard deviation is 10%. The Inter-CD for 95.5 wt. % of the polymer is 20 wt. % ethylene for such a sample.
(b) Intra-CD is the compositional variation, in terms of ethylene, within a copolymer chain. It is expressed as the minimum difference in weight (wt.) % ethylene that exists between two portions of a single copolymer chain, each portion comprising at least 5 weight % of the chain.
(c) Molecular weight distribution (MWD) is a measure of the range of molecular weights within a given copolymer sample. It is characterized in terms of at least one of the ratios of weight average to number average molecular weight, M.sub.w /M.sub.n, and Z average to weight average molecular weight, M.sub.z /M.sub.w, where ##EQU1##
Ni the number of molecules of weight Mi.
(d) Viscosity Index (V.I.) is the ability of a lubricating oil to accommodate increases in temperature with a minimum decrease in viscosity. The greater this ability, the higher the V.I.
Ethylene-propylene copolymers, particularly elastomers, are important commercial products. Two basic types of ethylene-propylene copolymers are commercially available. Ethylene-propylene copolymers (EPM) are saturated compounds requiring vulcanization with free radical generators such as organic peroxides. Ethylene-propylene terpolymers (EPDM) contain a small amount of non-conjugated diolefin, such as dicyclopentadiene; 1,4-hexadiene or ethylidene norbornene, which provides sufficient unsaturation to permit vulcanization with sulfur. Such polymers that include at least two monomers, i.e., EPM and EPDM, will hereinafter be collectively referred to as copolymers.
These copolymers have outstanding resistance to weathering, good heat aging properties and the ability to be compounded with large quantities of fillers and plasticizers, resulting in low cost compounds which are particularly useful in automotive and industrial mechanical goods applications. Typical automotive uses are in tire sidewalls, inner tubes, radiator and heater hose, vacuum tubing, weather stripping and sponge doorseals, and as Viscosity Index (V.I.) improvers for lubricating oil compositions. Typical mechanical uses are in appliances, industrial and garden hoses, both molded and extruded sponge parts, gaskets and seals, and conveyor belt covers. These copolymers also find use in adhesives, appliance parts, hoses and gaskets, wire and cable insulation, and plastics blending.
As can be seen from the above, based on their respective properties, EPM and EPDM find many, varied uses. It is known that the properties of such copolymers which make them suited for use in a particular application are, in turn, determined by their composition and structure. For example, the ultimate properties of an EPM or EPDM copolymer are determined by such factors as composition, compositional distribution, sequence distribution, molecular weight, and molecular weight distribution (MWD).
The efficiency of peroxide curing depends on composition. As the ethylene level increases, it can be shown that the "chemical" crosslinks per peroxide molecule increase. Ethylene content also influences the rheological and processing properties, because crystallinity, which acts as physical crosslinks, can be introduced. The crystallinity present at very high ethylene contents may hinder processability, and may make the cured product too "hard" at temperatures below the crystalline melting point to be useful as a rubber.
Milling behavior of EPM or EPDM copolymers varies radically with MWD. Narrow MWD copolymers crumble on a mill, whereas broad MWD materials will band under conditions encountered in normal processing operations. At the shear rates encountered in processing equipment, broader MWD copolymer has a substantially lower viscosity than narrower MWD polymer of the same weight average molecular weight.
Thus, there exists a continuing need for discovering polymers with unique properties and compositions. This is easily exemplified with reference to the area of V.I. improvers for lubricating oils.
A motor oil should not be too viscous at low temperatures so as to avoid serious frictional losses, facilitate cold starting, and provide free oil circulation right from engine startup. On the other hand, it should not be too thin at working temperatures so as to avoid excessive engine wear and excessive oil consumption. It is most desirable to employ a lubricating oil which experiences the least viscosity change with changes in temperature.
The ability of a lubricating oil to accommodate increases in temperature with a minimum decrease in viscosity is indicated by its Viscosity Index (V.I.). The greater this ability, the higher the V.I.
Polymeric additives have been extensively used in lubricating oil compositions to impart desirable viscosity temperature characteristics to the compositions. For example, lubricating oil compositions which use EPM or EPDM copolymers or, more generally, ethylene --(C.sub.3 -C.sub.18) alpha-olefin copolymers, as V.I. improvers are well known. These additives are designed to permit formulation of lubricating oils so that changes in viscosity occurring with variations in temperature are kept as small as possible. Lubricating oils containing such polymeric additives can better maintain their viscosity at higher temperatures, while at the same time maintaining desirable low viscosity fluidity at engine starting temperatures.
Two important properties (although not the only required properties as is known) of these additives relate to low temperature performance and shear stability. Low temperature performance relates to maintaining low viscosity at very low temperatures, while shear stability relates to the resistance of the polymeric additives to being broken down into smaller chains.
Ideally, preferred V.I. improvers are polymers which have good shear stability. These polymers generally have low thickening efficiency and low molecular weight. However, generally, low molecular weight polymers have low bulk viscosity and exhibit cold flow. They are difficult to handle in the conventional rubber processing plant.
It has been found that when operated carefully certain reactors can be used to polymerize alpha-olefins so as to enhance their various properties on a selective basis to suit their intended use. Reactors which are most suitable within the context of the instant invention are mix-free tubular and batch reactors.
Representative prior art dealing with tubular reactors to make copolymers are as follows:
In "Polymerization of ethylene and propylene to amorphous copolymers with catalysts of vanadium oxychloride and alkyl aluminum halides"; E. Junghanns, A. Gumboldt and G. Bier; Makromol. Chem., v. 58 (12/12/62): 18-42, the use of a tubular reactor to produce ethylene-propylene copolymer is disclosed in which the composition varies along the chain length. More specifically, this reference discloses the production in a tubular reactor of amorphous ethylene-propylene copolymers using Ziegler catalysts prepared from vanadium compound and aluminum alkyl. It is disclosed that at the beginning of the tube ethylene is preferentially polymerized, and if no additional make-up of the monomer mixture is made during the polymerization, the concentration of monomers changes in favor of propylene along the tube. It is further disclosed that since these changes in concentrations take place during chain propagation, copolymer chains are produced which contain more ethylene on one end than at the other end. It is also disclosed that copolymers made in a tube are chemically non-uniform, but fairly uniform as regards molecular weight distribution. Using the data reported in their FIG. 17 for copolymer prepared in the tube, it was estimated that the M.sub. w /M.sub.n ratio for this copolymer was 1.6, and from their FIG. 18 that the intermolecular compositional dispersity (Inter-CD, explained in detail below) of this copolymer was greater than 15%.
"Laminar Flow Polymerization of EPDM Polymer"; J. F. Wehner; ACS Symposium Series 65 (1978); pp 140-152 discloses the results of computer simulation work undertaken to determine the effect of tubular reactor solution polymerization with Ziegler catalysts on the molecular weight distribution of the polymer product. The specific polymer simulated was an elastomeric terpolymer of ethylene-propylene-1,4-hexadiene. On page 149, it is stated that since the monomers have different reactivities, a polymer of varying composition is obtained as the monomers are depleted. However, whether the composition varies inter- or intramolecularly is not distinguished. In Table III on page 148, various polymers having M.sub.w M.sub.n of about 1.3 are predicted. In the third paragraph on page 144, it is stated that as the tube diameter increases, the polymer molecular weight is too low to be of practical interest, and it is predicted that the reactor will plug. It is implied in the first paragraph on page 149 that the compositional dispersity produced in a tube would be detrimental to product quality.
U.S. Pat. No. 3,681,306 to Wehner is drawn to a process for producing ethylene/higher alpha-olefin copolymers having good processability, by polymerization in at least two consecutive reaction stages. According to this reference, this two-stage process provides a simple polymerization process that permits tailor-making ethylene/alpha-olefin copolymers having predetermined properties, particularly those contributing to processability in commercial applications such as cold-flow, high green strength and millability. According to this reference, the inventive process is particularly adapted for producing elastomeric copolymers, such as ethylene/propylene/5-ethylidene-2-norbornene, using any of the coordination catalysts useful for making EPDM. The preferred process uses one tubular reactor followed by one pot reactor. However, it is also disclosed that one tubular reactor could be used, but operated at different reaction conditions to simulate two stages. As is seen from column 2, lines 14-20, the inventive process makes polymer of broader MWD than those made in a single stage reactor. Although intermediate polymer from the first (pipeline) reactor is disclosed as having a ratio of M.sub.w /M.sub.n of about 2, as disclosed in column 5, lines 54-57, the final polymers produced by the inventive process have an M.sub.w /M.sub.n of 2.4 to 5.
U.S. Pat. No. 3,625,658 to Closon discloses a closed circuit tubular reactor apparatus with high recirculation rates of the reactants, which can be used to make elastomers of ethylene and propylene. With particular reference to FIG. 1, a hinged support 10 for vertical leg 1 of the reactor allows for horizontal expansion of the bottom leg thereof and prevent harmful deformations due to thermal expansions, particularly those experienced during reactor clean out.
U.S. Pat. No. 4,065,520 to Bailey et al. discloses the use a of batch reactor to make ethylene copolymer, including elastomers, having broad compositional distributions. Several feed tanks for the reactor are arranged in series, with the feed to each being varied to make the polymer. The products made have crystalline to semi-crystalline to amorphous regions and gradient changes in between. The catalyst system can use vanadium compounds alone or in combination with titanium compound and is exemplified by vanadium oxy-trichloride and diisobutyl aluminum chloride. In all examples titanium compounds are used. In several examples hydrogen and diethyl zinc, known transfer agents, are used. The polymer chains produced have a compositionally dispersed first length and uniform second length. Subsequent lengths have various other compositional distributions.
In "Estimation of Long-Chain Branching in Ethylene-Propylene Terpolymers from Infinite-Dilution Viscoelastic Properties"; Y. Mitsuda, J. Schrag, and J. Ferry; J. Appl. Pol. Sci., 18, 193 (1974) narrow MWD copolymers of ethylene-propylene are disclosed. For example, in Table II on page 198, EPDM copolymers are disclosed which have M.sub.w /M.sub.n of from 1.19 to 1.32.
In "The Effect of Molecular Weight and Molecular Weight Distribution on the Non-Newtonian Behavior of Ethylene-Propylene-Diene Polymers" Trans. Soc. Rheol., 14, 83 (1970); C. K. Shih, a whole series of compositionally homogeneous fractions were prepared and disclosed. For example, the data in Table I discloses polymer Sample B having a high degree of homogeneity. Also, based on the reported data, the MWD of the sample is very narrow. However, the polymers are not disclosed as having intramolecular dispersity.
Representative prior art dealing with ethylene-alpha-olefin copolymers as lubricating oil additives are as follows:
U.S. Pat. No. 3,697,429 to Engel et al. discloses a blend of ethylene-propylene copolymers having different ethylene contents, i.e., a first copolymer of 40-83 wt. % ethylene and M.sub.w /M.sub.n less than about 4.0 (preferably less than 2.6, e.g. 2.2) and a second copolymer of 3-70 wt. % ethylene and M.sub.w /M.sub.n less than 4.0, with the content of the first differing from the second by at least 4 wt. % ethylene. These blends, when used as V.I. improvers in lubricating oils, provide suitable low temperature viscosity properties with minimal adverse interaction between the oil pour depressant and the ethylene-propylene copolymer.
U.S. Pat. No. 3,522,180 discloses copolymers of ethylene and propylene, having a number average molecular weight of 10,000 to 40,000 and a propylene content of 20 to 70 mole percent, as V.I. improvers in lube oils. The preferred M.sub.w /M.sub.n of these copolymers is less than about 4.0.
U.S. Pat. No. 3,691,078 to Johnston et al. discloses the use of ethylene-propylene copolymers containing 25-55 wt. % ethylene, which have a pendent index of 18-33 and an average pendent size not exceeding 20 carbon atoms, as lube oil additives. The M.sub.w /M.sub.n is less than about 8. These additives impart to the oil good low temperature properties with respect to viscosity without adversely affecting pour point depressants.
U.S. Pat. No. 3,551,336 to Jacobson et al. discloses the use of ethylene copolymers of 60-80 mole % ethylene, having no more than 1.3 wt. % of a polymer fraction which is insoluble in normal decane at 55.degree. C., as oil additives. Minimization of this decane-insoluble fraction in the polymer reduces the tendency of the polymer to form haze in the oil, which haze is evidence of low temperature instability probably caused by adverse interaction with pour depressant additives. The M.sub.w /M.sub.n of these copolymers is "suprisingly narrow" and is less than about 4.0, preferably less than 2.6, e.g., 2.2.
In the case of viscosity index improvers, random cross-linking is neither a necessary nor desirable characteristic of the polymer. Illustrative of the patents dealing with unsaturated branched ethylene ter- and tetrapolymers in U.S. Pat. No. 3,790,480. Polymers of ethylene, C.sub.3 -C.sub.18 higher alpha-olefins and two classes of dienes are taught, the dienes having double bonds of the same or different polymerizability. In one class of dienes represented by 1,4-hexadiene, only one of the double bonds is readily polymerizable by the catalyst used. In another class of which 2,5-norbornadiene is representative, both double bonds are polymerizable utilizing the polymerization process of the patent. It is taught that the preferred viscosity index improvers are ethylene tetrapolymers wherein both classes of double bonds are used. Such polymers contain diene along the full length of the chain and are not nodularly branched. Random branching does not improve shear stability at a given TE in the effective manner of nodular branching.
Presumably, superior properties are achieved because use of a diene with two active double bonds results in long chain branching, with a concomitant increase in bulk viscosity of the polymer, but without any significant increase intrinsic viscosity or thickening efficiency. Increased bulk viscosity facilitates the manufacture and storage of the polymer. The catalyst used for polymerization is a Ziegler type catalyst. Both double bonds of the 2,5-norbornadiene are polymerizable by the Ziegler catalyst. The other diene, 1,4-hexadiene, however, has only one Ziegler catalyst polymerizable double bond. Hence, the polymers include a minor amount of unsaturation.